1. Field of the Invention
The invention pertains to a self-pumping hydropneumatic spring strut with internal level control, especially for use in motor vehicles.
2. Description of the Related Art
Self-hydropneumatic spring struts are already known. For example, in DE 101 04 358 C1, FIGS. 7 and 8 show a high-pressure chamber connected to a flow connection located in a piston rod guide. A filling bore is located in an outer tube and lines up with the flow connection before the piston rod guide is fully installed. After the piston rod guide has been inserted axially into the outer tube, the filling bore is closed off by the piston rod guide. A closed envelope body of variable shape is provided as a high-pressure chamber. The wall of the envelope body includes a gas-tight barrier layer.
With this configuration, internal parts, such as the high-pressure chamber, a piston, a piston rod, and a pump rod can be introduced axially into the outer tube of the spring strut, together with the piston rod guide. The spring strut is functional after at least the high-pressure chamber is filled with a pressurized gas via the filling bore. After the piston rod guide together with the working cylinder and other internal parts are further inserted into the outer tube, the filling bore is closed off by the piston rod guide. After the outer tube is been flanged over, the spring strut is completely assembled.
To allow this axial insertion of the piston rod guide, the seal between the piston rod guide and the piston rod is subjected to an appropriately high degree of pretension. This means that a correspondingly large amount of friction is present. A highly stressed single seal of this type tends to lead to leakage to the atmosphere, because the seal must withstand all the internal pressure.